ellsworth



Jan. 24, 1956 c. E. ELLSWORTH 2,732,472

RESONANT HIGH-FREQUENCY HEATING APPL'ICATOR Filed Feb. 26, 1953 3 Sheets-Sheet 1 Jan. 24, 1956 c. E. ELLSWORTH 2,732,472

RESONANT HIGH-FREQUENCY HEATING APPLICATOR Filed Feb. 26, 1953 5 Sheets-Sheet 2 Jan. 24, 1956 c swo H 2,732,472

RESONANT HIGH-FREQUENCY HEATING APPLICATOR Filed Feb. 26, 1953 3 Sheets-Sheet 5 Fig. 4

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I ,lllllllllllIllllhlllllllllllllll I United States Patent F 2,732,472 RESONANT HIGH-FREQUENCY HEATING APPLICATOR Carl E. Ellsworth, Anchorage, Ky., assignor, by mesne assignments, to National Cylinder Gas Company, Cl1icago, 11]., a corporation of Delaware Application February 26, 1953, Serial No. 339,054 6 Claims. (Cl. 219-10.55)

This invention relates to improvements in resonant high-frequency heating applicators, and more particularly to an electrically conductive structure which provides a predominant part of the inductance for the resonant applicator and which is electrically connected to an associated heating electrode. The primary object of the invention is to provide an improved conductive structure which will permit a maximum mutual inductance coupling between the structure and a coupling loop.

In copending application, Serial No. 138,628, Warren, filed January 14, 1950, now abandoned in favor of Warr'ens continuation-impart application, Serial No. 419,633, filed March 26, 1954, there are disclosed certain forms of resonant applicators which comprise an electrically conductive enclosure, in the form of a tunnel, within which are generated both magnetic and electric fields of great intensity. A predominant portion of the inductance of such applicators is provided by at least one electrically conductive structure or fin electrically connected to at least one wall of the enclosure and about which structure the aforesaid magnetic field is produced. The electric field extends between two spaced electrodes, one of which is electrically connected to the free end of the conductive structure. The spaced electrodes provide the predominant portion of the capacitance of the applicator. A coupling loop is positioned within a space encircling the conductive structure to transfer high-frequency power to or from the applicator or tunnel.

In order to maintain substantially constant the voltage between the applicator electrodes despite changes in power factor of a load disposed between them, the mutual inductance between the coupling loop and the conductive structure should be supra-optimum. As more fully explained in the aforesaid Warren applications, such changes in power factor occur due to changes with heating of the load and, in the case of a conveyor-fed applicator, to variation in the number of load objects being heated. When the mutual inductance is supraoptimum, i. e., appreciably larger than an optimum value, a substantial change in power factor of the load pro duces only a relatively small change in electrode voltage whereas with an infra-optimum coupling, the electrode voltage changes very rapidly with change in power factor.

Supra-optimum coupling may readily beattained in those cases where the applicator is of substantial width, for example, when the work being treated is of the size of a large foam-rubber mattress. However, where the applicator is designed for dielectrically heating narrow work, the attainment of supra-optimum coupling presents diificult problems.

An arrangement for supraoptimum coupling is set forth in copending U. S. application Serial No. 339,007, Sweets, filed February 26, 1953, wherein a conductive structure is provided with a recess for receiving a coupling loop. The present invention represents a further development of the generic invention described and claimed in the aforesaid Sweets application.

In accordance with the present invention, which is an improvement in the conductive structure or fin disclosed in the aforesaid Sweets application and certain of the conductive structures disclosed in the aforesaid Warren applications Serial Nos. 138,628 and 419,633 and also the copending Warren application Serial No. 419,071, filed March 26, 1954, which latter also is a continuation- 2,732,472 Patented Jan. 24, 1956 in-part of said Warren application Serial No. 138,628, a resonant high-frequency heating applicator comprised of an enclosure having electrically conductive walls is provided with an electrode within the enclosure in spaced relation to all of said walls and representative of essentially all of the capacitance of the resonant applicator. An electrically conductive structure is electrically connected at opposite ends, respectively, to the electrode and to the enclosure of the applicator to provide essentially all of the inductance of the resonant applicator. The conductive structure is of reduced thickness inter-, mediate its vertically extending edges or sides to provide a recess for receiving a coupling loop so that substantially all of the magnetic field within the applicator passes through the-coupling loop, to provide for supra-optimum mutual inductive coupling. More particularly, the conductive structure may be comprised of a pair of hollow columns interconnected by an intermediate tangential web member to provide the recess or concavity extending parallel with the flow of current therein and adapted for receiving a side of the coupling loop.

The invention further resides in features of construction, combination and arrangement hereinafter described and claimed.

For a more complete understanding of the invention, reference is made to the accompanying drawings, in which:

Fig. 1 is a perspective view partially broken away illustrating a resonant high-frequency heating applicator embodying the present invention;

Fig. 2 is a cross sectional view of a resonant highfrequency heating applicator disclosing a means for raising and lowering the electrode to accommodate work of varying height and schematically illustrating a typical oscillator used in conjunction with the resonant applicator;

Fig. 3 is a top plan view of the conductive structure or fin;

Fig. 4 is a side elevational view of the conductive structure partially in section to illustrate a specific type of construction;

Fig. 5 is a cross sectional view taken along a line substantially corresponding to line S5 of Fig. 4;

Fig. 6 is a side elevational view of the means for raising and lowering the electrode; and

Fig. 7 illustrates a means for indicating the position of the electrode and safety switches to limit the extent to which the electrode is raised or lowered.

Referring now to the drawings, wherein like reference numerals designate the same parts throughout the several views, and more particularly to Fig. 1, there is disclosed a resonant high-frequency heating applicator 10 comprised of electrically conductive walls 11-14 and having mounted therein elements or components providing substantially all the inductance and capacitance of the applicator. Only a small portion of the center section of the applicator is shown in order to preserve clarity in the drawings, it being understood that in the case of typical applicators, the walls extend beyond the ends of the apparatus contained therein. Although the applicator may be completely open at both ends, it is preferably a more complete enclosure to minimize leakage of the intense magnetic and electric fields existing therein.

Substantially all of the inductance for the applicator in the illustrated embodiment is provided by an electrically conductive structure 20 which may be secured or otherwise electrically connected to a supporting member and depends therefrom spaced from wall structure of the applicator. The length of the structure 20 from the connected endtc the depending end is small as compared to a quarter-wavelength of the frequency ofcurrent passing therethrough. The conductive inductance structure may be treated as a lumped inductance in which the current gradient is negligible in avoidance of the existence of standing waves.

The heating of a load within the applicator is effected by a high-frequency electric field existing between an electrode 30 and a conveyor 31 (Fig. 2) when the applicator is excited. The metallic conveyor 31 serves as the lower heating electrode so as to provide for a continuous processing of work. If desired, the conveyor may be removed and the function of a lower electrode served by the wall 13. The applicator is excited by a coupling loop 40 to create the high-frequency magnetic field circulating about the conductive structure 20. The loop 45) may be in the plate circuit of a high power oscillator tube whose resonant tank circuit is formed by the applicator. The coupling loop may be a wide band or strap of copper fastened to the outside of a loop-form provided by copper piping which serves to conduct cooling liquid for the oscillator tube, a construction claimed in copending Warren application Serial No. 419,074, filed March 26, 1954.

A suitable oscillator circuit is shown in Fig. 2 so that the purposes and advantages of the invention may be better understood. The anode of the tube 41 is connected to one terminal of the loop 40 whose other terminal is connected to a wall of the applicator grounded at 10a.

A direct-current source of high voltage 13+, B is connected between ground and the cathode of the tube 41, the positive end of that terminal being grounded as indicated. The grid of tube 41 is connected to the electrode 39 through an adjustable capacitor 42. The capacitor 42 and a capacitor 43, in whole or in part provided by the effective input capacitance of tube 41, provide a capacitive potential divider which, as explained in the aforesaid Warren applications Serial Nos. 138,628 and 419,633, is utilized in the automatic stabilization of the grid voltage. A direct-current path between the grid and cathode of tube 41 is provided by radio-frequency choke 44 and grid leak resistor 45.

As set forth above, it is desirable to maintain the voltage at the electrode 30 substantially constant despite variations in power factor within the applicator as produced by variations in load. To do so requires supra-optimum coupling between the coupling loop 40 and the conductive structure 20. As set forth in the aforementioned Sweets application, this condition will always be attained when substantially all of the magnetic field circulating about the conductive structure 2t) is coupled with or cut by the loop 40. i In some instances it is necessary to reduce the electrode voltage to a required lower value. Supra-optimum coupling aids in securing such voltage reduction. Limitations as to the percentage of the magnetic field coupled by the loop are presented by the width of the applicator enclosure, the permissive proximity between a leading side of the loop 40 with respect to the structure and the electrode which introduces the danger of fiashover. That fiashover may readily occur between the electrode 39 and the loop if the distance therebetween is greatly diminished becomes apparent when it is realized that the highfrequency voltage difference between the loop and the electrode may be as high as 32,000 volts, or even more.

In accordance with the present invention, the conductive structure 26 is provided with a recess or concavity 21 which is defined in part by adjacent walls of two opposite columns 22 and 23. The columns may be solid in cross section or hollow; preferably the latter in order-to reduce the weight of the structure and also for economical reasons. The space between the columns 22 and 23 is closed off by a tangential plate section 24 which is attached to the columns to form an integral unit therewith. In addition to forming an integral structure with the columns, the tangential or center section 24 provides a shield for preventing the loop 41} from being simultaneously exposed to magnetic flux traveling in opposite directions relative to the loop. The center section 24 is tangential to, i. e., itlies in the plane of the rearmost panels or surfaces so that the flux field follows a smooth unobstructed guide passage. The smooth surface of the fin 2t) prevents the concentration of currents produced by abrupt changes in the surface of a fin exposed to a magnetic field. The structure 2%) as defined may be formed from a single sheet of conductive material, such as aluminum or beryllium copper, but preferably is formed of smaller sections inasmuch as the conductive structure is of a very large size. The sections may be joined together by any well known method, such as welding or riveting.

The construction of the conductive structure 20 is such as to avoid sharp edges or corners in providing that all end surfaces exposed in the magnetic field circulating about the structure be gradually rounded, thereby providing for a more even distribution of current passing through the structure. With an even distribution of current, there is avoided the overheating of any given section of the conductive structure 29 as would occur should the ends terminate in sharp edges or corners.

A specific construction of the fin or conductive structure 29 is illustrated in Figs. 3-5. As shown in the preferred construction, the fin 2t? is comprised of a plurality of sheet metal sections joined together in any well known manner about a central frame structure including a plurality of channel frames 25 and securely mounted to the under side of an elongated member 26. The member 26 is constructed of sheet metal being reenforced along its inner surface by a longitudinal L-strut 27 extending from one end to the other. The ends of the member 26 terminate in box-like sections 28 and 29, the outer surfaces of which are curvilinear. The hollow upper member 26 is partially enclosed by a plate 26a extending intermediate the ends therof and to which are secured the reenforcing channel frames 25. In substance, the entire fin 20 may be said to be comprised of a channel framework about which is formed conductive sheet metal. The internal framework is not traversed by the heavy radio-frequency currents of the resonant applicator and may therefore be of material and shape selected to afford the required mechanical strength without regard to its conductivity or effect upon the distribution of current. The electrode 39, Fig. l, is mounted to the depending end of the conductive structure or fin 2% by way of a plate 32 which .is mounted on a reenforcing channel frame 33. Conductive sheet metal is formed about the reenforcing framework to provide the electrode surface 34. It will be observed that the ends and sides of the electrode terminate in curved surfaces in order to avoid the possibility of fiashover due to corona effects. Like the conductive structure Zll, the electrode 36 is substantially a hollow structure formed about the central reenforcing framework 33.

The shortest distance from any common point of the structure 20 and the electrode 34 to the adjacent edges or sides of the electrode may be made small as compared to a quarter-wavelength at the frequency of voltage on the electrode. The electrode may be treated as a lumped capacitance providing substantially all the capacitance of the applicator. With such an arrangement the voltage at all points on the electrode will be substantially uniform.

A particular applicator embodying the invention produces about 20 kilowatts at frequencies of the order of 30 megacycles. In such applicator, the dimensions of the fin 20 are approximately 2 feet in the direction of current flow, 9 feet long and 9 inches wide.

The operative structure of the applicator which is comprised of the conductive structure 26 and electrode 30 may be raised and lowered so as to vary the distance between the upper electrode 30 and the lower electrode or conveyor 31 by means of an elevating mechanism 50, as illustrated in Figs. 2 and 6. Such adjustment permits selection of the voltage gradient through the work to be dielectrioally heated. Cables 51, which may be of metal strands, are secured to the plate 26a by ring bolts 52 and pass through suitable apertures in the upper wall or roof 11 of the applicator enclosure and over rollers 54 mounted on tne upper surface of the wall. The cables terminate on capstan rollers cr spools 55. The rollers 55 are driven by a prime mover 56 mechanically coupled therewith through a difierential and reduction gear system contained within the enclosure 57, a gear and sprocket chain mechanism 53, and reduction gears 59. The spools or rollers 55 are mounted for rotation on shafts 55a which terminate at opposite ends at the differential and reduction gear mechanism 57 and bearing mounts 60 secured to the roof or top wall 11 or". the applicator enclosure. The slack in the cables 51 and the slope of the electrode 3 relative to electrode 31 may be adjusted by way of turn buckles 61 located intermediate the ends of the cables.

The distance between the upper and lower electrodes 36 and 31 of the applicator may be visually observed by means of an indicator 7%, Fi 7. The indicator "it"? in cludes a graduated scale "/1 mounted on the flange of the enclosure ill) and a pointer 72 mechanically coupled to the roof member 26a of the conductive structure 21 The pointer '72 is mounted on an angular rod 73 secured at one end to a vertical cylindrical post 74 which is secured on the aforesaid roof member 25a. Adjustments of the pointer may be effected relative to the electrode in order to provide an exact indication of the distance between the upper and lower electrodes 39 and 31 by a collar 75 which may be slidably adjusted along the length of the post id and locked in any desired position by means of a set-screw.

In order to limit the upp r and lower travel of the electrode 3 3 and thereby avoid contact between the upper and lower electrodes, there are provided limit switches till disposed on opposite sides, above and below, the collar '75 and mounted on the flange of a channel member 76.

The conductive structure 2b is electrically connected to the side walls 12 and 14 of the applicator, Fig. 2, by way of thin flexible sheets 81 of conductive material, such as beryllium copper, which extend along the entire length of the fin and preferably about the entire periphery thereof. This conductive sheet material serves to carry the current to the conductive or fin structure 2:"; from the conductive walls of the applicator and in addition provides a shield to prevent the leakage of the intense magnetic field into the area above the conductive structure. Because of absence of any high-frequency field in the area so isolated, it is not necessary to include insulation in the lifting mechanism 5 3 which may, as shown, contact both the conductive tin and the walls of the applicator.

What is claimed is:

1. A high-frequency heating applicator comprising a pair of electrodes supported in spaced relation one from the other, at least one of said electrodes being long and narrow, conductive structure electrically connected at one end to said one of said electrodes and extending away from said one electrode, a high-frequency magnetic field of said applicator being concentrated about said conductive structure and a high-frequency electric field being concentrated between said electrodes, a housing enclosing said structure and the space between said electrodes, means including walls of said housing electrically interconnecting the other end of said conductive structure with the other of said electrodes, said conductive structure comprised of a pair of spaced parallel columns, each of them compared to its width being relatively long lengthwise of said one electrode, and an interconnecting plate member tangential with said columns to form a concavity between said columns, and a coupling loop extending transversely of said conductive structure and at least in part within the concavity to provide enhanced mutual coupling between said conductive structure and said loop.

2. The high-frequency heating applicator of claim 1 wherein the concavity in a direction away from said electrodes extends from one end of said conductive structure to the other.

3. A high-frequency heating applicator comprising a pair of electrodes supported in spaced relation one from the other, at least one of soil electrodes being long and narrow, conductive structure electrically connected at one end to said one of said electrodes and extending away from said one electrode, a housing enclosing said structure and the space between said electrodes, means including walls of said housing electrically interconnecting the other end of said conductive structure with the other of said electrodes, said applicator being resonant at a frequc cy predominantly determined by the inductonce of said conductive structure and the capacity between said electrodes, said conductive structure being substantially U-shaped in cross-section transverse to the direction of current flowing therethrough, each side portion of said structure comprising a column which along the length of said one electrode is long compared to its width, said columns of said conductive structure having rounded side portions to reduce the concentrations of current flowing therein, and a coupling loop in part disposed within the open portion of said U-shaped conductive structure.

4. A high-frequency heating applicator comprising elongate spaced electrodes for receiving dielectric material to be heated, a shielding enclosure having conductive wall structure, conductive structure within said enclosure and cooperating with said wall structure electrically to interconnect said electrodes, said conductive structure being narrow and long in a direction of elongation of said electrodes, said conductive structure conprised of two spaced hollow columns together making up a substantial length of said structure and defining between them a narrow recess extending in the direction of current flow along said structure, a conductive member tangentially disposed with respect to said columns and interconnecting them, and a coupling loop having at least a portion thereof positioned within said recess between said columns for linkage with a high-frequency magnetic field circulating about said conductive structure.

5. A high-frequency heating applicator as in claim 1 in which said electrodes are variably spaced, means for raising and lowering one of said electrodes, said means extending through a top wall of said enclosure and attached to said conductive structure, and flexible conductive means extending between a top portion of said conductive structure and side walls of said enclosure for shielding said raising and lowering means from the magnetic field.

6. A high-frequency heating applicator comprising elongate variably spaced electrodes for receiving dielectric material to be heated, a shielding enclosure having conductive wall structure, a conductive structure within said enclosure and cooperating with said wall structure electrically to interconnect said electrodes, said conductive structure being narrow and long in a direction of elongation of said electrodes, said conductive structure comprised of two spaced hollow columns together making up a substantial length of said structure and interconnected by a conductive member tangentially disposed with repect thereto, means for raising and lowering one of said electrodes, said means extending through a top wall of said enclosure and attached to said conductive structure, and flexible conductive means extending between a top portion of said conductive structure and side walls of said enclosure for shielding said raising and lowering means from a magnetic field circulating about said conductive structure.

References Cited in the file of this patent UNITED STATES PATENTS 2,124,029 Conklin July 19, 1938 2,215,582 Goldstine Sept. 24, 1940 2,506,626 Zottu May 9, 1950 2,563,585 Dallenbach Aug. 7, 1951 

